Process for preparing active from of manganese dioxide



Patented Aug. ze, 1952 2,608,466.

UNITED. STATES PATENT OFFICE;

ibrahamL. Fox, Washington, D. C., assigner` tor y ReginalddS. DeanfWashington, D. C.

o Drawing', Application. Deiueinberl,` 1948',

Serial No. 65,5740 f 4 Claims. v(c1. 23-145) i l This invention relates to an active form of polarized light shows that allparticles arecrys; manganese dioxide and processesfor preparing talline. X-ray spectrometry shows onlythelatf it. It has for its aim the provision of a new form tice .parameters of rhodocrosite and ,examination of manganese dioxide having properties making with the electron.` microscope shows polyhedral it especially1 suitable for use asma depolarizerin 5 crystals of. an average diameter of` Z-micronse dry., cells, `for the oxidation ot` organic chemical This material ispinl; in "color vand `stable in air compounds and for other purposes., at-room temperature. Themanganese canbonate L The manganese Adirnride of thisV invention is is heated inairto 570 F; and the material anar especially suitable for use in dry cells ofthe Le lyzed at several periods with the following rer- Clanche type. This arises fromthe fact that 10 sults: it combines a higher electrical conductivity than Time (mn heretofore known with great reactivity as re-` 10 40 vealed by initial capacity and high stability as e 60 revealed by long shelf life of batteries. loon-:nui Tn? ture of the improved battery oxide of this invene I f tion starts in all cases with the preparation of a Examination of the product under the electron fully crystalline precipitated manganese car-` microscope shows the product to have a particle bonate having a crystal size from 0.25 micron to size. of 2 microns average diameter.

6 microns average diameter. The oxidation of 20 manganese carbonate has been heretofore em- Example II ployed for the manuf'actureoi .battery oxide but 11.1;ake50 gramsof manganous carbonate hav- With ldilerent results. It iS .YIIDOlJl that the ingcompletely crystalline particles 0.25 micron preoioitatedoarbonate be free from amorphous in diameter. Thismaterial is pnkin eclo'r'and material and havethe crystal structure of rhodo- 25 Stable in dry air. The manganese carbonateis @rosita the individual Crystals boina Within the heated to 300 F. in air and the material' analyzed Size range stated. Such mangaHGSerarbOIwJG at several periods with the following results. will not appreciably darken in` air lateroom tem- ,L peratures even` when stored over long periods. Tlme (hours): Per' cent M1102 Manganese carbonate precipitates cfiner crystal 30 size darken when` stored in'` air and coarse par-'- I ticles, such as may bemade by grinding natural v i rhodocrosite, do notoxidize readily enough on y .....fr-f-rfe-f-e-G heat-'mg' prefer tp make thee manganese caff' Examination of` the product under `theelectron bonatefoniltpmctlce ,OfmYmVent-lon fromcom" 35 microscope shows'thepartcle size to be thatfi' plFX. animomlaal 501111519115 m'the manne!" Whlh thecrystals ofthe carbonate used namely, about will be set forth later. Any manganese carbonate 0,;25rmcm meeting the herein stated requirements may. however, be satisfactorily used. Themanguanese Examplel. dioxide produced by the pmce 0f .my HVGHOT? 40 `l' take 100 grams of? manganese carbonate Wm 'have the Same particle Size. as the Crystal precipitated from aV complex manganese ammonia Size 91 the manganese cabona'teffom WhCh it is solution in `accordancewith` the procedure` dee mada J scribed later herein. Thismaterial is'fullycrys- In the practice or my lnvention I` take. this tallineand has a grain size of 2` microns diameter. manganese carbonate and heat 1t 1n air within 45 I` fuier but do notwash this materal so' thaifit the temperature range 30W-600 F. for a SufCleflt is `saturated` with ammonia andiammonium car-.- mme t0 p'QduCe a product @Cmamng from 50* bonate. This material is dried in airandturns 70% M1192 y i y black. .Itis then ynearest in air abaco? fel-..24 The time necessary to accomplish this result hours; .'*The resulting. product analyzes 64% depends 0n the temperatur@ At 500 F- it is 50 MnOz. It diiiersvfromethe.products of theepre.-V about 2 hours and at 3 90" F- 1t 1S 21190Wl 15 hOUlS- ceding examples,- lhowever. in that the particle Heatms for al? eddltlonal time has `very little sizeef'the manganeseidioxide.iene.longer that effect on the oxide. j y of the :originalmanganese carbonate-crystals but The fOllOWl'Ils eXm'ples `are given aslllustffatve isveryimuch smaller, lbeing in-this instaneeonly of this embodiment of `my; invention; 55 (p25 mcmm.`

" Eampze Toincreaseflthe M nOz content of the` prod 4 j "l ucts-of the foregoingexamples I- iindthatthey I take lllgrams of manganese carbonatehavmay toe leached` with dilute acids which` forni ing a composition manganese 44.3%, carbon soluble manganese saltssuch as sulphuric or @19eme 43l6 %1;vate7f26% Examinationguhder GQ nitric acidsor. with.. ammonium salts of such 3 acids which dissolve MnO, such as ammonium chloride'V or sulphate. After such leaching the MnOz is washed with water until after boiling one gram with 100 cc. of water, a pH of more than four is reached. This requires exhaustive washing. The following examples are given as illustrative of this embodiment of my invention.

Example IV I take 100 grams of precipitated manganese carbonate, fully crystalline, stable in air and Example V I take 100 grams of manganese carbonate prepared by decomposition of complex ammoni-a manganese carbonate solution by ceiling, and having'a crystal size of 2 microns, and heat in air for-'24 hours at 475 F. This p-roduct analyzes:

Per cent MIlOz 69.0 Mn 59.3 MnO 20.3

State of oxidation MnOmss.

This material is leached with enough 10% H2SO4 to combine with the MnO. The leached product is filtered, wash-ed and dried. It contains by analysis:

Y Per cent M1102 87.4: Mn 60.5 Mn() 6.8

State vof oxidation MnOrci.

CO2,A This carbonated product may be further l oxidized by heating in the same temperature range as before, with the result that the manganese is further oxidized.

This procedure may be repeated a number of times ywith an increase in the MnOz at each step. This increase is approximately 40% of the unoXidized manganese remaining so that the increment` of manganese oxidation obtained by thentreatment is less for each succeeding step. Thus, if the partially oxidized material contains 69% MnOz and 20.3 MnO, as in Example V, the rst treatment will leave about 12% MnO, the secondabout 8% and the third about 6%. After these three treatments, the state of oxidation of the manganese will beV about Mn01.92.

The amount of CO2 required is the stoichiometric equivalent of the'MnO present. However, as the reaction is slow, an excess of at least is passed through the slurry. The carbonation process can be considerably expedited by conducting it under a pressure of several atmospheres. As illustrative of this embodiment of my invention, I give the following examples:

Example VI I take 100 grams of the product of Example I containing 65% MnOa This is 'made into a slurry with water containing 20% solids. It is carbonated by passing CO2 through the violently agitated slurry for 15 minutes at such a rate that 50% excess over the stoichiometric equivalent of the 22.1% MnO present in the sample is passed through the solution. The slurry is then filtered, washed, dried and reoxidized. The resulting product contains 75.9% M1102 and 58.0% Mn. This gives a ratio of Mn as MnOz/Mn of 82.8%.

An additional carbonation and reoxidizing gives v a product having a ratio Mn as MnO2::Mn of 89.7%. This product contains 2.2% H2O.

Example VII I take 100 giams of the product `'f Example 11 containing 64% MnOa I make this into a slurry with water and pass in CO2 lunder 200 pounds/square inch pressure with agitation. I allow the reaction to proceed until no further CO2 is absorbed. This takes only about 10 minutes. The carbonated product is filtered, washed and dried. It is then heated in air for 24 hours at 470 F. and the carbonation and oxidation procedures repeated. The final product analyzes as follows:

Per cent Mn 62.8 MnOz 90.8 MnO 7.0 H2O 4.5

State of oxidation MnOrsis.

ing to the method described, as determined by the standard method of the Signal Corps, ranges from 7-9. It is accordingly well within the requirement of a pI-I higher than 4.0.

My` invention for the improvement of the manganese dioxide content of materials containing essentially MnOz and MnO in a ratio of at least one molecule of MnOz to one of MnO by carbonation and oxidation by heating in airis applicable to such mixtures formed in other ways than the heating of carbonate as set forth in the preceding examples.

Such mixtures of MnO and MnO2 may, for example, be formed by partially reducing natural or articial MnOz. This may be accomplished by heating in air or in a reducing gas. The lower the temperature at which such partial reduction is carried out, the easier is the carbonation. As illustrative of this embodiment of my invention, I give the following examples:

Example VIII I take 100 grams of pure MnOz made by the decomposition of manganese nitrate. I heat this for 5 minutes at 400 C. in a stream of hydrogen. The resulting product analyzes 60.2% MnOz. I make a, slurry of this product with water and pass in CO2 with stirring under 100 pounds per square inch pressure until no further CO2 is absorbed. The carbonated material is washed. dried and heated at 470 F. for 24 hours. -The carbonation and heating steps are repeated once.

the following analysis:

Per cent Mn 62.8 M1102 90.8 M110 7.0 H2O 2.2 State of oxidation MnOrsis.

Example IX I take 100 grams of a natural manganese ore containing 90.5% M1102 -200 mesh. I heat this for `5 minutes in air at 750 C. The resultant product contains 78.1% MnO2. I make a slurry of this product with 80% water and pass in CO2 with stirring until no further CO2 is absorbed. This product is ltered, washed and dried and heated in air for 24 hours at 470 F. The resulting product contains 88.2% MnOz. l

The properties of such manganese dioxide, particularly as they relate to its value as a battery oxide, depend especially on its particle size. This, i-n turn, is determined by the particle sizeof the carbonate from which it is prepared. In carrying out my invention I prefer to control the crystal size of the manganese carbonate. This I can do by precipitating the carbonate fromthe complex formed by dissolving MnO in solutions of ammonia and ammonium carbamate-carbonate mixtures. This may be done lby either dilution or heating, both of which shift the equilibrium from carbamate to carbonate. The higher the temperature and the greater the concentration of ammonia and ammonium carbonate in the solution from which the carbonate is precipitated, the larger will be the crystal size.

The following examples are given as illustrative of this embodiment of my invention:

Example X Per cent Mn 44.3 CO2 43.6 H2O 7.3

The crystal size is about 2 microns average diameter.

Example XI I make the same solution as in Example X but instead of heating in an open vessel, I heat the solution in a pressure-tight vessel to 90 C. for one hour. Ninety-ve percent of the manganese in the solution is precipitated as carbonate. This carbonate is filtered and washed. It is stable in air and has the following analysis:

Per cent Mn 44.8 CO2 44.1 H2O 6.3

The crystal size is about 5 microns average diameter.

Example XII I prepare the solution as in the previous two examples. I then dilute it with an equal volume of Water and heat in a closed vessel for 6 hours at 75 C. Eighty-five percent of the manganese is precipitated as carbonate. The carbonate is ltered, washed with water and dried. It is stable in air and has the following analysis:

Per cent Mn 44.0 CO2 43.3 H20' I; 7.9

The crystal size is 0.25 micron average diameter.

Regardless of the particle size, the manganese dioxide of rmy invention has new and important properties making it valuable as a battery oxide. The electrical resistance of the battery oxide of my invention is less than that of heretofore known battery oxides. The vspecific resistance of the product of this invention varies from about 2000` to about 6000 ohm cm. For the purpose of comparison` I have made measurements in the Vsame way on Gold Coast ore of battery grade and lined a resistance of 80,000, 30,000 for oresV activated by acid leaching, 500,000 for precipitated amorphous oxides and 10,000 to 12,000 for electrolytically prepared battery oxides.

It should be understood that the high electrical conductivity of the battery oxide is only obtained if all the steps of any embodiment of my invention are carried out. For example. the oxidation of manganese carbonate in accordance with my process does not yield a highly conducting oxide. The high conductivity is only conferred by the second step of leaching with acid or carbonating and reoxidizlng. Carbonation and reoxidation is especially effective in this connection. Such treatment in a typical example decreases the speciiic resistance from about 100,000 ohms to 3,000 ohms.

The battery oxide of my invention is characterized by the so-called y structure` as determined by X-ray spectrometry. Lattice parameters and intensities of a typical product of the present invention are as follows:

d, ngstroms: Intensity, relative Examination of the product by the electron microscope shows anhedral rounded somewhat porous particles of approximately uniform size.

The relationship of initial battery discharge capacity to particle size for the battery oxide of this invention is shown in the following table:

Discharge Average Average Particle Size l Resistance, Vtlg e Initial Clfalgy hms g Capacity Mg .Micron 0.25 "A" 166. 2/3 1. 13 110. 90. 2.0 165. 2/3 1. 13 95. 0 Y 93. s 5.0 21" 166. 2/3 1. 13 88. 0 88. 0

The cells were of standard The tests were at 70 F.

What is claimed is: 1. The method of producing a manganese Le Clanche type.

oxide suitable for depolarization of dry cells which includes the steps of partially oxidizing completely crystalline vprecipitated manganese carbonate of a particle ,size .25 to 6 microns by `heating in an atmosphere containing oxygen to a temperature from 300 to 600 F. carbonatin'g said oxidized carbonate by treatment with carbon dioxide and water, and then further oxidizing the carbonated product by heating to a temperature of 300 to. 600 F. in an atmosphere containing oxygen; Y

2.'jProcess of improving therbattery grade of a manganese oxide product corresponding in oxygen contentto a mixture of MnOz and MnO in which the molecular ratio of MnOz Ato MnO is at least 1:1, which comprises carbonating the manganese oxide product by treating the same inthe presence of Awater with carbon dioxide in an amount substantially in excess of the stoichiometrical equivalent of the calculated MnO content of the starting material, and subjecting the carbonated product to oxidation treatment by 'heating it to a temperature of from 300 to 600 F. in an atmosphere containing free oxygen 8 substantially to increase the oxygen content of the product. l

3. The process defined in claim 2, in which the carbonation step is conducted under a pressure of several atmospheres. l f

4. The process defined in claim 2, in which the carbonation and re-oxidation stepsV are re` peated at least once.

ABRAHAM L. FOX.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name l Date 1,275,566 Ellis et al. Aug. 13, 1918 1,293,463 Kaplan Feb..4:, 1919 1,448,110 v De Olaneta Mar. 13, 1923 1,761,133 Laury June 3, 1930 1,889,021 Kobe Nov. 29, 1932 1,947,457 Bradley Feb. 20, 1934 1,988,799 Kato Jan. 22, 1935 2,123,250 Muller et al. July 12, 1938 

1. THE METHOD OF PRODUCING A MANGANESE OXIDE SUITABLE FOR DEPOLARIZATION OF DRY CELLS WHICH INCLUDES THE STEPS OF PARTIALLY OXIDIZING COMPLETELY CRYSTALLINE PRECIPITATED MANGANESE CARBONATE OF A PARTICLE SIZE .25 TO 6 MICRONS BY HEATING IN AN ATMOPHERE CONTAINING OXYGEN TO A TEMPERATURE FROM 300* TO 600* F. CARBONATING SAID OXIDIZED CARBONATE BY TREATMENT WITH CARBON DIOXIDE AND WATER, AND THEN FURTHER OXIDIZING THE CARBONATED PRODUCT BY HEATING TO A TEMPERATURE OF 300* TO 600* F. CARBONATCONTAINING OXYGEN. 